This invention relates to rotary electrical contacts and seals for horizontally mounted rotating machines, and more particularly to liquid metal, rotary electrical contacts combined with a convertible rubbing face seal and labyrinth seal that is effected by axial movement of the rotor.
Prior art machines have almost exclusively employed graphite brushes rubbing against metal commutators as the means for forming sliding electrical contacts. Liquid metal contacts offer several advantages over brush-commutator systems, including lower voltage requirements, higher current-carrying capability, and lower frictional and I.sup.2 R heating losses. In spite of these advantages, very few machines have been built which use liquid metal contacts, except for hompolar electrical generators used for research purposes.
The problems associated with generators are not the same as for motors because generators are not stopped or started frequently, and generally rotate in only one direction. However, similar precautions have to be taken during start-up of both generators and motors. But, because a motor is frequently started, stopped, and reversed, the use of prior art liquid metal contracts would be impracticably cumbersome. Thus, there has been little use of such contacts for motors. As stated above, one of the serious difficulties associated with the use of liquid metal rotary electrical contacts has been their inability to maintain continuity of the electrical circuit under all conditions of rotational speed including stopping, starting, and reversing of the machine. Another difficulty has been the chemical reactivity of the liquid metals with atmospheric gasses. Further, wear particles from machine materials and other contaminants can cause chemical changes in the liquid metal and render it unfit for use after only a limited time. Still another difficulty is the possible leakage of the liquid metal from the machine into the environment. Most conductive liquid metals are severe pollutants, such as mercury. Some materials, such as sodium-potassium (Nak) alloys, are particularly objectionable contaminants and difficult to use because of their corrosive and pyrophoric nature. Therefore, there is a need for a nearly perfect seal when using liquid metal high current rotary contacts.